Conventionally, it has been known that, when mandibular opening and closing movements are impaired by a temporomandibular disorder or fracture of jaw, mandibular opening and closing movements are performed by using a mouth-opening training device to restore the mandibular functions. The human jaws function by a combination of: a rotational movement, in which the mandible rotates in relation to the maxilla around the temporomandibular joint as a fulcrum; and an anterior sliding movement, in which the mandible moves back and forth in relation to the maxilla, when the mandibular condyle of the temporomandibular joint slides back and forth. In line with this, a mouth-opening training device for training both of a rotational movement and an anterior sliding movement of the mandible has been proposed (refer to Patent Document 1).
According to the mouth-opening training device of Patent Document 1, an upper lever in contact with the maxilla is connected to a lower lever in contact with the mandible; the levers are opened and closed in relation to each other around a connecting portion as a fulcrum, thereby training the mouth-opening movements based on a rotational movement of the temporomandibular joint; in which a latching mechanism for moving the lower lever back and forth in relation to the upper lever is provided, so that an anterior sliding movement of the temporomandibular joint can be trained. This latching mechanism is composed of: a handgrip gear portion including a handgrip connected to a gear; and a rack portion engaging with the gear. The lower lever moves back and forth in relation to the upper lever by rotating the handgrip.
In the mouth-opening training device according to Patent Document 1, the upper and lower levers for training the mouth-opening movements based on a rotational movement of the temporomandibular joint are provided separately from the handgrip for training an anterior sliding movement of the temporomandibular joint; therefore, when the device is actually used, the rotational movement and the anterior sliding movement are performed separately as independent movements. Also, since the connecting portion is provided at the center of the rotational movement, the device guides the mandible in an arc that is reverse to the trajectory of the mouth-opening movement of the actual mandible that rotates around the temporomandibular joint.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2000-33104